I have a row house with a "flat roof" meaning it actually has a small grade so that water runs off the back. However, towards the middle of the roof there is a depression that allows an inch deep puddle to form after a rain. I believe the depression is caused by a the settling of the roof from the weight of the roof deck. We have recently had a leak due to the puddle and so I did a fairly thorough job patching and putting a fresh layer of roofing cement down in the entire area that collects a puddle that is about 2 feet by 6 feet. It is a rolled rubber roof. I understand that all this may mean I should probably start planning on replacing the roof in the future but I'm looking for a medium term improvement for the puddle.
I was talking to the hardware store employee and he suggested putting play sand down fill the depression and then put a layer of the rolled rubber down to flatten it out. That seems like a reasonable way to fill the irregular form of the space but does that seem like an ok medium term solution?